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<div>Richie said Dec 4 23:01:12 CET 2020</div>
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<div>“ I'd recommend a passive RC lowpass filter between the output of the op-amp and the ADC input. It can serve several purposes:</div>
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<div>1. . . . . . . 6. “</div>
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<div>Reason 7: A typical anti-aliasing filter is often reflexively supposed to be an even-order active low-pass with an op-amp output feeding directly to the sampler. While the supposed audio bandwidth may be only, say, 20kHz the op-amp’s inherent output noise
may extend to several MHz, and once sampled, be FOLDED AND ADDED many times back to the audio (baseband) range. </div>
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<div>Accordingly, it is often advisable (as Richie suggests) to have an odd order active filter with the real pole passive and last; and set for low impedance, so that no op-amp buffer is even needed – the RC junction feeding the sampler directly.
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<div>Such practice being common with analog delays, CCDs (BBDs).</div>
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<div>-Bernie</div>
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